Measuring Prop Pitch at Home FIXING

[hwsiii]

This is an easy way to measure the pitch of your prop at home instead of having to go to a prop shop and pay them. The following items will be needed to do this:

A. Carpenters Square
B. Compass
C. Protractor

Normally prop pitch is measured at about 70% of the Radius of the prop. When you have a progressive or regressive pitch prop you can normally not get the right pitch because these props have a variable pitch across the blade of the prop, but if you subtract 1" from progressive props and add 1" for regressive props it will normally be right. On a normal prop you will get the right pitch.

The prop that is being used for this example is a 10 5/8" x 12" 15 degree rake prop with 3" inches of progressive pitch. It is called a 12" Pitch prop but it is actually 11" of pitch on the leading edge with 13" on the trailing edge, that is why you subtract 1" from the answer.







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[junior1113]

Re: Measuring Prop Pitch at Home

Re: Measuring Prop Pitch at Home

wow thats easy lol.

 

[hwsiii]

Re: Measuring Prop Pitch at Home

Re: Measuring Prop Pitch at Home

Good, I am glad you like it junior.

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[tkmichael11]

Re: Measuring Prop Pitch at Home

Re: Measuring Prop Pitch at Home

I think I'll just look on the box.

 

[BigJ08]

Re: Measuring Prop Pitch at Home

Re: Measuring Prop Pitch at Home

This is really helpful as my prop has no markings indicating it's size. Thanks!

 

[hwsiii]

Re: Measuring Prop Pitch at Home

Re: Measuring Prop Pitch at Home

I am glad it was helpful J.


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[Bifflefan]

Re: Measuring Prop Pitch at Home

Re: Measuring Prop Pitch at Home

I have 3 props, i that im sure of the pitch and 2 not so sure. I meassured all 3 and got the answers. My new factory J/E 17p meassured out to be a 13.98.
my new SST 19p meassured out at 14 and change, and the Michigan wheel prop came out at 20p.

I took the in and found the right numbers.
J/E 14x17p
SST 13x19p
Mich Wheel 13.5x15

I did the calc's on each of these 3 times, following the directions to the "T".
Is there a step in the process that didnt get posted? Or is this just for some props?

 

[hwsiii]

Re: Measuring Prop Pitch at Home

Re: Measuring Prop Pitch at Home

Biffle, would you please show me your exact calculations step by step, and the numbers you used, so I can see exactly how you did it. And I will try to figure out what is wrong.


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[Bifflefan]

Re: Measuring Prop Pitch at Home

Re: Measuring Prop Pitch at Home

I will. Ill try to get them on late tonight or early tomorrow. Thanks

 

[hwsiii]

Re: Measuring Prop Pitch at Home

Re: Measuring Prop Pitch at Home

You are very welcome Biffle.


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[mswalter2009]

Re: Measuring Prop Pitch at Home

Re: Measuring Prop Pitch at Home

That's complicated. I'm just looking for the right prop that will produce the WOT rpms recommended by the manufacturer. Variable pitch prop??? Jeez. I just installed a 2008 90hp Yamaha 2-stroke on a 18' bay (type) boat. How many of 90s have been sold since 2006. (when they changed the model). About a million. Someone must have figured this out before?

My problem, I think, is that my engine is mounted too low. There are some great posts on this site and some very knowledgable posters. Thanks. According to prop calculators changing pitch by a degree only makes a slight difference in RPM. Therefore, start with a prop size/pitch that is "normal", work with your engine mounting height, get it so that WOT is somewhat close, then work on the prop size pitch.

A thought - do pilots go through this when they want to re-prop their single engine Cessana?

 

[Bifflefan]

Re: Measuring Prop Pitch at Home

Re: Measuring Prop Pitch at Home

Ok, got some figures for you,
J/E 14x17p cast on the prop.

dia 14
radius 7
70% = 4.9 (used 4 15/16 to draw circle)
trailing edge is 5.5
leading is 3.125
diff is 2.375
seperation is 65 deg

5.5-3.125=2.375
2.375x360=855/65=13.15

These are the numbers that i had writen down. the others were from memory.

 

[Bifflefan]

Re: Measuring Prop Pitch at Home

Re: Measuring Prop Pitch at Home

That's complicated. I'm just looking for the right prop that will produce the WOT rpms recommended by the manufacturer. Variable pitch prop??? Jeez. I just installed a 2008 90hp Yamaha 2-stroke on a 18' bay (type) boat. How many of 90s have been sold since 2006. (when they changed the model). About a million. Someone must have figured this out before?

My problem, I think, is that my engine is mounted too low. There are some great posts on this site and some very knowledgable posters. Thanks. According to prop calculators changing pitch by a degree only makes a slight difference in RPM. Therefore, start with a prop size/pitch that is "normal", work with your engine mounting height, get it so that WOT is somewhat close, then work on the prop size pitch.

A thought - do pilots go through this when they want to re-prop their single engine Cessana?

This thread is about finding the pitch of a prop that has no markings. not about reproping a motor. There is tons of reading on that subject.

 

[hwsiii]

Re: Measuring Prop Pitch at Home- FIXING Hopefully

Re: Measuring Prop Pitch at Home- FIXING Hopefully

Biffle, that should have worked. I am going to take this down and go back over it and see what the problem is. Evidently it is my fault, not yours.



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[Bifflefan]

Re: Measuring Prop Pitch at Home FIXING

Cool, Let me know when you have something. Im into problem solving. I just like a good challange i guess. Math problems are the best. But ill take what ever comes along.

 

[hwsiii]

Re: Measuring Prop Pitch at Home FIXING

You and me both Biffle, I tried it on two different props I have here and I got the right pitch both times. Both were progressive pitch and they came out just right, I just had to subtract 1" for the progressive pitch. One was 12" pitch and the other was a 14" pitch, but your numbers weren't even close, so i have a third prop I wil get and try tonight hopefully.
Thank you for letting me know of the problem, I appreciate it.


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[Rowroy]

Re: Measuring Prop Pitch at Home FIXING

This method is a bunch of crap. I tried it on my jet boat and it didn't work worth at all!!